1. Field of the Invention
The present invention relates to surface acoustic wave devices for use in, for example, resonators, bandpass filters, and other devices, and a method for making the same. More particularly, the present invention relates to a surface acoustic wave device having a structure covered by an outer resin and a method for making the same.
2. Description of the Related Art
FIG. 8 is a cross-sectional view of an exemplary conventional surface acoustic wave device. The surface acoustic wave device 101 has a packaging structure including a substrate 102 and an outer resin layer 103. Electrodes 102a and 102b are provided on the upper surface of the substrate 102 for electrically connecting the surface acoustic wave element 104 to an outer package. A surface acoustic wave element 104 is fixed on the substrate 102 via an insulating adhesive material 105. The surface acoustic wave element 104 is electrically connected to the electrodes 102a and 102b via bonding wires 106a and 106b. A space A must be formed around the surface acoustic wave element 104 to facilitate vibration thereof, and the surface acoustic wave element 104 thereby exhibits satisfactory characteristics. In order to define the space A, the surface acoustic wave element is surrounded by a metal cap 107 having an opening at the bottom. The metal cap 107 is fixed on the substrate 102 via an adhesive 108. Moreover, an outer resin layer 103 is disposed around the metal cap 107 to enhance moisture resistance.
Reductions in size, profile and cost are required for surface acoustic wave devices, as with other electronic components.
In the surface acoustic wave device 101, the package is composed of the substrate 102, the metal cap 107, and the outer resin layer 103. Thus, the package requires many components, which causes an inevitable increase in production cost. Furthermore, after the metal cap 107 is provided to define the space A, the protective layer 109 must be formed by resin molding. This process precludes reductions in size and profile.
In order to overcome the problems described above, preferred embodiments of the present invention provide a surface acoustic wave device and a method of making the same, which provide a surface acoustic wave device that has a greatly reduced size and profile and that is much less expensive to manufacture.
According to a first preferred embodiment of the present invention, a surface acoustic wave device includes a substrate, a surface acoustic wave element mounted on the substrate, the substrate being provided with at least one first groove provided in the substrate and located at the exterior of the surface acoustic wave element, a flexible resin layer provided on the substrate inside of the first groove so as to cover the surface acoustic wave element, the flexible resin layer being relatively soft, and an outer resin layer provided at the exterior of the flexible resin layer, the outer resin layer being harder than the flexible resin layer.
In this surface acoustic wave device, the package structure includes the substrate, the flexible resin layer, and the outer resin layer. This SAW element packaging structure including these resinous materials facilitates reductions in size and profile of the surface acoustic wave device, whereas conventional surface acoustic wave devices using metal caps for providing spaces preclude reductions in size and profile.
Since the package is completed by forming the resin layers without using a metal cap, the number of components and material cost are reduced and the manufacturing process is simplified. Accordingly, the surface acoustic wave device is produced at low cost.
Since the flexible resin layer provided on the substrate does not extend outside of the first grooves, the flexible resin layer is reliably covered by the outer resin layer, thereby providing a surface acoustic wave device having superior environmental resistance.
Preferably, at least one pair of first grooves opposing each other is provided on the substrate so as to sandwich the surface acoustic wave element.
In such a case, these first grooves are preferably formed at both sides of the SAW element. Thus, the outer resin layer can be formed at both sides of the flexible resin layer, providing a surface acoustic wave device having superior moisture resistance.
The surface acoustic wave device according to another preferred embodiment of the present invention may further include electrodes provided on the substrate for connection with an external component, and bonding wires for electrically connecting the electrodes and the surface acoustic wave element, wherein the surface acoustic wave device is fixed to the substrate.
Alternatively, the surface acoustic wave device may further include electrodes disposed on the substrate for electrical connection with an external component, wherein the surface acoustic wave element is fixed on the substrate by a face down mounting process, and is electrically connected to the electrodes.
That is, the SAW element and the electrodes on the substrate may be bonded with bonding wires or electrically connected by a face down mounting process. Since the bonding wires and the conductive bond are covered with the flexible resin layer in any bonding process, reliability of electrical connection is greatly improved.
Preferably, the surface acoustic wave device may also further include a moisture resistant material layer provided at the exterior of the outer resin layer, the moisture resistant material having higher moisture resistance than that of the outer resin layer.
The moisture resistant material layer contributes to further improvements in environmental properties such as moisture resistance of the resulting surface acoustic wave device.
The surface acoustic wave device may further include another electronic component mounted on the substrate and covered by the outer resin layer.
In such a configuration, reductions in size, profile, and costs of a composite surface acoustic wave device including ICs and other elements are achieved.
According to another preferred embodiment of the present invention, a method for making surface acoustic wave devices includes the steps of preparing a mother substrate having a plurality of first grooves on the upper surface thereof, mounting surface acoustic wave elements onto the mother substrate so that the first grooves are located at the exterior of the surface acoustic wave elements, forming a flexible resin layer of a relatively soft resin on the substrate closer to the surface acoustic wave element than the first grooves so as to cover each surface acoustic wave element, covering the flexible resin layer with an outer resin layer of a relatively hard resin, and cutting the outer resin layer and the mother substrate into individual surface acoustic wave devices.
The method including these simplified steps provides inexpensive surface acoustic wave devices having a greatly reduced size and a greatly reduced profile.
Preferably, the first grooves are at least one pair of first grooves formed at both sides of each surface acoustic wave element.
In such a manner, the outer resin layer is reliably formed at both sides of the flexible resin layer.
Preferably, the method further includes the step of forming second grooves, each extending from the outer resin layer to the mother substrate at outer portions of the first grooves after the formation of the outer resin layer, wherein the mother substrate is cut along the second grooves into the individual surface acoustic wave devices in the cutting step.
The mother substrate is readily cut into surface acoustic wave devices at the second grooves.
Preferably, the method further includes the step of covering the outer resin layer with a moisture resistant material having higher moisture resistance than that of the outer resin layer, this covering step being performed after the step of forming the second grooves and before the step of cutting the mother substrate into the individual surface acoustic wave devices.
Since the outer surface of the outer resin layer is covered by the moisture resistant material layer, the resulting surface acoustic wave device exhibits higher moisture resistance.
Preferably, the mother substrate has third grooves for facilitating cutting at the cutting positions into the individual surface acoustic wave devices on the lower surface thereof.
According to another preferred embodiment of the present invention, a communication device includes the surface acoustic wave device according to the other preferred embodiments of the present invention.
Other features, characteristics, elements and advantages of the present invention will become apparent from the following detailed description of preferred embodiments of the present invention with reference to the attached drawings.